There exists a variety of two-dimensional ultrasonic imaging apparatus. Such apparatus is used in various medical disciplines, such as cardiology, radiology and obstetrics. In the field of obstetrics, apparatus having a very large installed base in the U.S.A. is the General Electric Model GE-3200. Other two-dimensional ultrasonic imaging apparatus is commercially available inter alia from ATL, a subsidiary of Phillips, Acuson, Toshiba Ultrasound, Siemens Ultrasound and Hewlett-Packard Ultrasound.
Three-dimensional ultrasonic imaging apparatus is also known and commercially available from 3-D Ultrasound Inc. of North Carolina, U.S.A.
Various mechanisms have been employed in an attempt to retrofit conventional two-dimensional ultrasonic imaging apparatus for use in providing three-dimensional ultrasonic images. These include, for example:
mechanical assemblies which constrain the motion of the ultrasonic probe and measure its position using rotary position encoders; PA1 electromagnetic position sensors which require an external field generator in the vicinity of the patient; PA1 optical position sensors which require mounting of cameras in the vicinity of the patient; PA1 acoustic position sensors which require transducers to be mounted onto the patient; and PA1 motor assemblies which move at least part of the probe at a constant rate which allows image position and orientation to have a fixed relationship to timing.
The following U.S. Patents are believed to be relevant to the general field of the present invention: U.S. Pat. Nos. 5,817,022; 5,398,691; and 4,932,414.